[JS IR] Support per-file mode and ES modules

js/js.translator/testData/box/esModules/jsName/jsTopLevelClashes.kt

@@ -0,0 +1,32 @@
+// DONT_TARGET_EXACT_BACKEND: JS
+// ES_MODULES
+// MODULE: main
+// FILE: lib.kt
+@file:JsModule("./foo.mjs")
+package lib
+
+@JsName("test")
+external val foo: Int
+
+// FILE: lib2.kt
+@file:JsModule("./bar.mjs")
+package lib
+
+@JsName("test")
+external val bar: Int
+
+// FILE: main.kt
+package main
+
+import lib.*
+
+fun box(): String {
+    if (foo != 23 || bar != 45) return "fail"
+    return "OK"
+}
+
+// FILE: foo.mjs
+export var test = 23;
+
+// FILE: bar.mjs
+export var test = 45;